1. Field of the Invention
The present invention relates to the field of fine chemicals and material science, and more particularly relates to a method of preparing UV-curable inkjet pigment ink for textile printing.
2. Description of the Related Art
Compared with the traditional textile printing technology, inkjet printing has many advantages. For instance, it is more suitable for small quantity and multi-species printing, and it can print in a wide spectrum of colors. As ink is a key consumable in textile digital printing, the research and development of the textile printing ink is very important for the application and advancement of textile digital printing. Compared to dye inks, textile inkjet printing with pigment ink has increased exponentially over the past years due to its numerous advantages, such as universal applicability to different textile substrates, reduction of water and energy expense, and most importantly, environmental friendliness.
The size and distribution of pigment particles is one of many factors that determines the quality of pigment ink. Big pigment particles can easily block the printer nozzle, and may cause serious diffuse reflection on the surface of textile, which adversely effects the brightness of printed textile. Different from paper printing, textile printing requires higher degree of rubbing and washing colorfastness. In order to increase colorfastness, a certain amount of binders are often added into the pigment ink to improve the adhesion of pigment to textiles. However, the presence of binders easily leads to deterioration of the ink fluency. To address the above problems in pigment ink, researchers worldwide have proposed many possible solutions. For example, Chinese patent CN103052694A discloses a method for preparing thermal inkjet printing pigment by mixing the pigment and polyurethane; China CN102847497A patent discloses a method of using pigment microcapsules to coat the surface of pigment so as to change their surface charge and improve the stability of water-based ink; Chinese patent Nos. CN1982383 and CN1850921 disclose a method for preparing an inkjet ink using nanoscale pigment capsules; Chinese patent No. CN102926224A discloses a method of using polymerizable dispersant and miniemulsion ink polymerization process to prepare an ink-jet pigment ink which requires no additional binder; U.S. Patent Nos. US005554739A and US006042643A provide a method of introducing a reactive functional group to the pigment surface to improve the colorfastness of the ink. US70301175 and U.S. Pat. No. 7,338,988 discloses a method of adding polyacrylate emulsion to aqueous pigment to improve the colorfastness of the inject pigment ink to PE, PVC, PU and other plastic material. However, the colorfastness problem is still yet to be fully solved.
UV-curable pigment ink is a novel pigment ink and its application in textile printing has gained worldwide attention. It offers many benefits such as energy saving, no solvent emissions, low pollution to the environment, high productivity and good color fastness. UV-curable ink is mainly composed of UV-curable resin, reactive diluents, photo initiators, colorants, additives and other components. Previous study of mini-emulsion polymerization reaction found that the monomer conversion rate is about 81% when using oil-soluble initiator to prepare mini-emulsion pigment particles. The presence of remaining monomer or oligomer in the pigment ink could be one reason that adversely affects the colorfastness. To increase the monomer conversion rate and improve the colorfastness, we combined thermal polymerization reagents, UV-curable reagents and mini-emulsion polymerization process to make a UV-curable pigment ink. First, monomers, photo initiators and thermal initiators are mixed with pigment particles to make a UV-curable pigment mini-emulsion paste. Secondly, the pigment paste is mixed with a water-soluble cosolvent, a non-ionic surfactant and other additives to obtain a UV-curable inkjet pigment ink. The results show that the UV-curable inkjet pigment ink of the invention has greatly improved the colorfastness.